I'm convinced my thermostat is stuck open again, it takes ages for the car to warm up.

The question is, how often do you find yourself replacing a thermostat? It seems like this is my third in 2 years...

_________________
1998 Rover Mk VII
2001 Honda CBR 929RR (street)
2014 BMW S1000RR (track)

If it's that often I'd look past the thermostat and into whether the engine needs a good flush or change of coolant. Somethings not agreeing with it.

It gets flushed with distilled water approx. once a year. When I flush it I just drain, fill, run, drain, fill run, until the distilled water comes out clear. Of course I make sure to run it long enough to open the thermostat, and I have the heater taps opened etc to really flush everything out.

I've never used any flushing agents, detergents or cleaners - just distilled water. Is it advisable to use product? Do you recommend one in particular?

_________________
1998 Rover Mk VII
2001 Honda CBR 929RR (street)
2014 BMW S1000RR (track)

You should be able to do some basic tests with the thermostat and a some boiling water in a pan (or other domestically approved container )

That should confirm if it is opening and closing or stuck.

What temperature thermostat are you fitting ? There are a few permutations on what temp they will open.

The other is what sort of temperature gauge do you have ? Is it just the standard electrical sender type - if so, may be worth testing how well that is working. Could be a sender fault.

I purchased a new thermostat recently. Tested it in a saucepan and it didn't open. Took it back and changed it over for a new one which tested fine!
I know it's the opposite of your issue (yours is open) but I think it's maybe related to a quality issue.
Yes, they are consumable but not the amount you've gone through.
It would be interesting to test your existing one out of the car!

_________________
Justin

The old thermostats were copper and brass. Recently some brands used SS instead. I have had a few of these fail, some open some closed.
You can still find brass/copper ones, look before you buy.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I've never had a problem with the brass ones...

_________________
67 Deluxe
Dry suspension
1293cc, 11:1 comp, RE 282 camshaft, 45 Weber, extractors etc
4 synchro close ratio gbox
Cooper S brakes, no booster
Stealth box, as Doc says "goes harder and idles!"
RH tank cos I needed it crossing the Nullarbor etc..

I have been into minis for over 50 years and have never trusted thermostats. Even in this day and age with all the electronic gizzmos for this and that, we still have this damm stupid thing.
When I got married in 1974, the bloody thing let me down on our honeymoon (in the same mini that I'm currently restoring). Didn't catch it quick enough a buggered up a real good motor.
The following may not be the exact way to do things but has worked for me. Since then I have run with a thermostat with the centre cut out and bypass plugged up. Appears to be enough back pressure for good circulation throughout the cooling system, good cooling in summer, good heating in winter, never given an ounce of trouble all these years.
Currently doing a major build and spending big on the engine, will still use the cut down thermostat.

I've had a few fail over the years...my advice, if the cooling system is relatively clean (power back flushed every now and then), good coolant, hoses good, rad good, fan/fanbelt OK and thermo operating...then invest in a good gauge and get used to watching when it seems to hit its regular operating point...glance at it regularly...

Late 60s I was welcomed to the wonderful world of jammed thermostats just out of Cardwell, early in the morning, 1/2 an hour into Highway speeds and the bonnet started spewing steam (I regularly scan gauges, so it happened quite quickly)

Cooked the head

https://en.wikipedia.org/wiki/Wax_thermostatic_element

_________________
"Show me the Mini!"

Thanks mate. Yeah, I am very, very aware of all the gauges all the time. This is the only reason I think it is stuck open, I never drive it until I can see a bit of temperature happening, and then I monitor the oil pressure closely until it is completely warmed up. Lately, it's taking ages to show any temp at all, and I'll drive a solid 3-5 km before it is up to normal operating temps.

New thermostat and gaskets on the way. When I open it up, I'll let everyone know if it was stuck open or not.

_________________
1998 Rover Mk VII
2001 Honda CBR 929RR (street)
2014 BMW S1000RR (track)

Just my experience, never had a failure but always run inhibited coolant. Upon dismantling for whatever reason, everything is always completely clean....

_________________
67 Deluxe
Dry suspension
1293cc, 11:1 comp, RE 282 camshaft, 45 Weber, extractors etc
4 synchro close ratio gbox
Cooper S brakes, no booster
Stealth box, as Doc says "goes harder and idles!"
RH tank cos I needed it crossing the Nullarbor etc..

Don't matter how clean it is...

they can and do fail...

if it does it on the Nullabor and you catch it early...just remove the thermostat to get you to a repairer...

_________________
"Show me the Mini!"

What is acceptable warm up time for the engine? I suspect my thermostat is stuck open. But it's only 2 years old and when I flushed my cooling system few months back, I tested it before putting it back in... My car last night in 14 deg C ambient temp took 5-10 mins to get up to temp... when i first installed it, I distantly remember seeing the temp drop slightly when it got to temp indicating the thermostat was opening up... no such thing at the moment.

A few minutes, 10-15 say...but why don't you take the thermostat out, pop it into a saucepan of water on the stove, heat it up and see what (if anything) happens...or just fit a new one and save your self $100s if you damage your engine...

_________________
"Show me the Mini!"

You should probably also check the gauge and sender to be certain they are not lying to you.

_________________
Cheers Dave.